base

Compute GradientDrawable's opacity correctly

The current implementation of GradientDrawable always assumes the shape needs
to be blended. This causes all windows to be considered translucent by default.
This change recomputes the opacity as needed to ensure windows are marked
opaque when they should.

Change-Id: Iaf291d889a6c5122ab00c9f5781df3e7f61547fa